Semiconductor devices with inductors

ABSTRACT

Semiconductor devices provided with high performance high-frequency circuits that reduce interference caused by inductors are provided. In the semiconductor device including a modulator circuit to modulate a carrier wave by a base band signal to output an RF signal and a demodulator circuit to demodulate the RF signal by use of the carrier wave to gain the base band signal and a local oscillator to generate the carrier wave, inductors respectively having a closed loop wire are adopted. Interference caused by mutual inductance is reduced by the closed loop wire. For example, where inductors are adopted in the modulator circuit, a closed loop wire is disposed around the outer periphery of the inductors.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP 2004-240569 filed on Aug. 20, 2004, the content of which is hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices with inductors, more specifically, relates to semiconductor devices suitable for high frequency circuits of a wireless communication device.

BACKGROUND OF THE INVENTION

An inductor in use for a circuit, in which high frequency signals in the vicinity of GHz band are received and transmitted, can be incorporated into a semiconductor device because of its smaller inductance. In this case, there are found some countermeasures against the setback brought by the fact that other inductors and wires, etc., are disposed closer to the inductor within a minute interior of the semiconductor device. For examples, such integrated circuit is disclosed in Patent Document 1 as a strip of well of high concentration and conductivity embedded in a semiconductor substrate disposed below an inductor for the purpose of reducing the overcurrent induced by the inductor formed on the upper surface of the semiconductor substrate and attenuating crosstalk effect to the inside of the substrate. Also, it is disclosed in Non-Patent Document 1 that inductors 5 and 8 provided with inputs 6 and 10 are respectively enclosed by grounded wires 7 and 9 large in width as shown in FIG. 13 in order to attenuate interference caused by the mutual inductance between two inductors. To note, in Non-Patent Document 2, the principle of the effect brought by the magnetic field created around the inductor is explained in reference to Biot-Savart law. Further, in Non-Patent Document 3, the drawing effect, in which the frequency of an oscillator using one inductor is changed by the effect brought by other inductors, is explained.

(Patent Document 1) Refer to Japanese Patent Application Laid-open No. 2003-249555.

(Non-Patent Document 1) Refer to ‘On-chip RF Isolation Techniques’ by Tallis Blalack and two others in USA and ‘IEEE BCTM 2002 Proceedings’ printed in 2002, p. 205 to p. 211.

(Non-Patent Document 2) Refer to ‘Physics Lecture Volume 5 on Electromagnetics’ by Hisao Kumagai and another, published in 1965 by Asakura Shoten Co., Ltd., p. 146.

(Non-Patent Document 3) Refer to ‘RE Microelectronics’ by Behzad Razavi, published in 2002 by Maruzen Corporation, p. 247.

SUMMARY OF THE INVENTION

Although an inductor, which is one of the fundamental passive elements of a circuit, is used widely for an oscillator, a filter, a matching circuit, a transformer and so forth, it is scarcely used for a semiconductor device produced by a common method because of its difficulty with gaining larger inductance. However, when a high-frequency circuit to be packaged in a portable wireless communication terminal is incorporated into a semiconductor device, an inductor can be formed with a practical layout area by use of the wiring techniques of the semiconductor device because an inductance required for such high frequency circuit is of lower value, so that plural inductors are feasible for use therein. The provision of the inductor allows an oscillator, a filter, a matching circuit, a modulator circuit and so forth to be integrated into one semiconductor device, which renders the semiconductor device multi-functional. In this way, an RF-IC (Radio Frequency-Integrated Circuit) is realized, where a high frequency circuit is incorporated into the semiconductor device, which circuit includes a modulator circuit in which a radio frequency signal (hereinafter, referred to as ‘RF signal’) is gained by subjecting a base band signal to modulation, a demodulator circuit operating to the contrary of the modulator circuit and a local oscillator to generate carrier waves used for modulation and demodulation.

The integration density of the semiconductor device becomes higher year by year due to cost reduction, in accordance with which plural inductors are disposed within one semiconductor device. Thus, it results in the inductors and the circuits being disposed nearby therein so that such problems occur as signals interference between inductors and interference between inductors and wires. The occurrence of such signals interference within the semiconductor device invites the malfunction of the circuits, the output of unwanted noise and the deterioration of the input sensitivity. Especially, for a wireless communication circuit including an RF-IC, there is a big difference in signal strength between carrier waves and received/transmitted signals so that large gap for isolation of about −70 dB is required between the local oscillator to generate carrier waves and the output circuit of RF signals.

In particular, in the case of an RF-IC in such direct conversion system as directly converting base band signals into radio frequency signals without the step of converting the former into intermediate frequency signals, it often happens that the frequency of the local oscillator signals and that of RF signals are almost the same or close to the multiple ratio relation. Thus, when there is interference between the local oscillator signals and the RF signals, serious intermodulation distortion and undesired disturbing waves leakage occur. It is hard to improve the signals by means of a filter once they are subjected to intermodulation distortion owing to interference, since there exist interference signal components within the same frequency band as the desired signals. Furthermore, if interference occurs through the route of a parasitic element, it is impossible to incorporate an element to hamper interference in the course of such route.

Accordingly, a technique is sought after that reduces interference caused by signal leakage among circuits generated within the semiconductor device. As mentioned earlier, in the Patent Document 1, such method is disclosed as blocking interference signals transmitted through the semiconductor substrate, but it cannot restrain the effect brought by the mutual inductance between inductors.

Mutual inductance occurs due to the magnetic fields change between two inductors. Inputting a high-frequency signal into an inductor generates an AC magnetic field, along with which an induced electromotive force occurs in the inductors and wires in the vicinity. An induced current caused by such induced electromotive force flows between circuits supposed to be isolated so as to turn into unwanted interference signals, which cause problems within the semiconductor device. Thus, the larger the mutual inductance is, the greater the degree of interference is.

The effect brought by magnetic fields generated in the vicinity of the inductors reduces as the distance between an observation point and the respective inductors increases, as disclosed in the Non-Patent Document 2 in reference to Biot-Savart law. Accordingly, countermeasures are conventionally taken such as establishing a wire prevention region in the surrounding of the respective inductors so as to separate inductors and wires from one another that are vulnerable to interference. However, such countermeasures have setbacks because such wire prevention region requires extra room in the semiconductor device so that it hampers integration density from increasing and prevents the layout size of the substrate from reducing.

Therefore, it is required to block signal transmission caused by magnetic fields fluctuation among inductors. For that purpose, in general, the respective inductors are enclosed by a conductive plate or box. In the structural arrangement of a semiconductor device, typically, either the upper and lower portions or one side of the respective inductors is enclosed by a conductive plate made of metal layers. However, in a standard semiconductor device, the interval between such metal layers becomes so narrow that large parasitic capacity occurs between the respective inductors and the corresponding conductive plates. Thus, the composite impedance of the respective inductors and such parasitic capacity turns out to be capacitive, which makes it hard to gain desired inductance.

The method as described in the Non-Patent Document 1 and as shown in FIG. 13 whereby the respective inductors are enclosed with grounded wires large in width and made of metal layers is feasible to attenuate interference caused by mutual inductance. However, this method has the following setbacks. The first problem is that the ground wires 7 and 9 shall be earthed in such an ideal manner that there is no potential fluctuation in those wires. For a semiconductor device, it is hard to make the impedance of the respective ground wires lower over wide range of frequency because there exists a parasitic element such as a bonding wire therein. Accordingly, signals with voltage amplitude occur even on such ground wires. Further, such ground wires act as a common terminal between circuits, so that the signals generated in one circuit or another easily interfere with the inductors. The second problem is that disposing a wire large in occupancy around the respective inductors for the purpose that the respective ground wires come closer to an ideal grounding condition causes parasitic capacity on a semiconductor substrate. As a result, an induced current generated on the respective ground wires becomes hard to flow to minimize the effect on interference attenuation brought by such induced current.

In the Non-Patent Document 1, for the convenience of measuring the amount of the signal transfer through the semiconductor substrate, two inductors respectively are isolated by enclosing them with the respective ground wires. For a semiconductor device, it is hard to isolate them by ground wires in view of restriction in the number of terminals incorporated and the stable operation of the circuits incorporated therein. Isolation by wider ground wires in order to lower impedance enlarges the layout area of the circuits and deteriorates their integration density.

The present invention is to provide a high-performance semiconductor device with high frequency circuits incorporated therein wherein interference between inductors is attenuated.

The semiconductor device according to the invention includes a first circuit to modulate a carrier wave by a first signal to output a second signal whose frequency is higher than that of the first signal; a second circuit to demodulate a third signal by the carrier wave to output a fourth signal whose frequency is lower than that of the third signal and a third circuit to generate the carrier wave, wherein at least one of the first through third circuits is provided with at least one inductor, and the one inductor is provided with a closed loop wire enclosing the one inductor.

As mentioned later, the enclosure around the respective inductors by the closed loop wire attenuates interference caused by mutual inductance. The above first through third circuits respectively are realized as a modulator circuit, a demodulator circuit and a local oscillator respectively, which circuits are made into high-frequency circuits, in which the inductors are provided. Even when such high-frequency circuits are integrated into one semiconductor device so that the respective circuits are disposed adjacently, the attenuation of interference caused among the circuits allows high-performance of such high-frequency circuits incorporated into a semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing the inductor used for the invented semiconductor devices;

FIG. 2 is a vertical view showing the inductor used for the invented semiconductor devices;

FIG. 3 is a figure showing the effect of reducing inductive coupling caused by the invented semiconductor devices;

FIG. 4 is a top view of the inductor for measurement to evaluate the effect of the invented semiconductor devices;

FIG. 5 is a curve graph showing the effect of the invention;

FIG. 6 is the second vertical view showing the inductor used for the invented semiconductor devices;

FIG. 7 is the third vertical view showing the inductor used for the invented semiconductor devices;

FIG. 8 is the second top view showing the inductor used for the invented semiconductor devices;

FIG. 9 is a circuit diagram showing a wireless communication circuit using the invented semiconductor devices;

FIG. 10 is a diagram showing the first embodiment for carrying out the invention;

FIG. 11 is a diagram showing the second embodiment for carrying out the invention;

FIG. 12 is a diagram showing the third embodiment for carrying out the invention; and

FIG. 13 is a top view showing the semiconductor devices using a conventional technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the semiconductor devices with high-frequency circuits according to the invention are described in more details with reference to the accompanying drawings. To note, the same reference numbers and words indicate the same or similar equivalents in FIGS. 1, 2 and 6 through 12.

To begin with, the arrangement of the respective inductors that are in use for the semiconductor devices according to the invention is explained with reference to FIG. 1. In the drawing, reference numerals 1, 2, 3 and 4 respectively indicate an interference source side inductor, an interfered side inductor, a wire for reducing the inductive coupling corresponding to the interference source side inductor and a wire for reducing the inductive coupling corresponding to the interfered side inductor. The wire 3 is disposed such that it circumscribes the inductor 1 to defined a closed loop wire. The wire is not limited to a square configuration, but may be curved, linear or the combination thereof. Likewise, the wire 4 is disposed such that it circumscribes the interfered side inductor 2 to define a closed loop wire.

Such connection is prohibited for the wires 3 and 4 as an AC signal flowing not only to the inductors 1 and 2, but also to any electrode of the circuit. To note, it is unfavorable to make stubs or slits on the respective wires 3 and 4 long enough to give an effect on the wavelength of a high-frequency signal flowing in the respective inductors. For example, when a slit pattern is inserted between the metal layers of the respective inductors and the substrate to prevent overcurrent from being generated on the substrate and the pattern is connected in such a manner that it goes around the respective inductors, parasitic capacity is generated between the respective inductors and the pattern. Thus, the electric current flowing the wire for reducing the inductive coupling is reduced and a favorable effect on interference reduction is spoiled.

FIG. 2 shows the vertical view of the inductor 1 taken along A-A line of FIG. 1. In FIG. 2, reference numerals 11, 12, 13 and 14 respectively indicate a wire crossing with the inductor 1 and the wire 3 for reducing the inductive coupling, a via made from a conductive material to vertically interconnect discrete metal layers and to connect the inductor 1 with the wire 3, an isolation layer and a semiconductor substrate respectively. It is shown therein that the inductor 1 and the wire 3 are formed in the same metal layer to maximize the effect for reducing the inductive coupling, but they are not necessarily formed in the same layer.

The principle according to which interference caused by the mutual inductance between the interference source side inductor 1 and the interfered side inductor 2 is attenuated is explained with reference to FIG. 3. FIG. 3 exemplifies the state where magnetic fields are generated in response to the configurations as shown in FIG. 1 and shows circular loops through which electric current flows. In the drawing, reference numerals 21, 22, 23 and 24 respectively indicate a loop according to the wire 3 of the interference source side for reducing the inductive coupling, a loop according to the inductor 1, a loop according to the wire 4 for reducing the inductive coupling and a loop according to the inductor 2.

Upon an alternating signal current 26 flowing through the loop 22 according to the inductor 1, an AC magnetic field 25 is generated. The direction of the field corresponds to a direction 31 which is vertical with regard to the surface formed by the loop 22 and to which a right-handed screw advances when the same turns to the direction of the current 26 in accordance with Biot-Savart law as shown in the Non-Patent Document 2. The AC magnetic field 25 changes to the opposite direction according as the direction and strength of the current 26 varies. The surface formed by the loop 21 according to the wire 3 is almost the same as that formed by the loop 22, so that under the influence of an AC magnetic field 31 an induced current 28 flows through the loop 21 according to the wire 3 in accordance with Lenz's law. The direction of the current 28 corresponds to the direction which generates a magnetic field to the direction 32 which offsets a magnetic field generated on the loop surface in accordance with Lenz's law. An AC magnetic field is generated to the vertical direction 33 with regard to the surface formed by the loop 24 according to the inductor 2. Based on Lenz's law as shown in the Non-Patent Document 2, an induced current 27 flows through the loop 24 by the inductor 2 while an induced current 29 flowing through the loop 23 by the wire 4. The direction to which the currents 27 and 29 flow corresponds to the direction which generates a magnetic field to the direction 34 that sets off the magnetic field 33.

Accordingly, the respective magnetic fields 32 and 34 generated by the respective induced currents 28 and 29 make the magnetic field 33 small. Thus, the induced current 27 which is an interference current generated in the inductor 2 is reduced by the induced currents 28 and 29. That is to say, the foregoing indicates that the input current 26 turns to the output induced current 27 through the magnetic fields 31, 25 and 33 so that transmitted interference signals are attenuated. The induced current 27 is generated by the mutual inductance between the inductors 1 and 2 so that the wires 3 of the interference source side for reducing the inductive coupling to generate the induced current 28 and the wire 4 of the interfered side for reducing the inductive coupling to generate the induced current 29 cooperatively attenuate interference caused by the mutual inductance between the inductors 1 and 2. To note, according to the above principle, disposing the wire for reducing the inductive coupling on one of the interference source side and the interfered side may be less effective than being disposed on both sides, but interference is reduced anyway.

The above effect on the interference attenuation is confirmed below with reference to the experimental results and the calculation results by electromagnetic analysis.

FIG. 4 shows a top view of the layout pattern prepared for making comparison by measurement between the case where the invention is incorporated and the case where the invention is not incorporated. In the drawing, reference numerals 41, 42, 43, 44, 45 and 46 and 47 respectively indicate an interference source side inductor, an interfered side inductor, a wire of the interference source side for reducing the inductive coupling, a wire of the interfered side for reducing the inductive coupling, a ground pad, an input pad and an output pad. The respective portions where the inductor 41 and the wire 43 intercross as well as the inductor 42 and the wire 44 intercross define two-tiered metal layers. The input pad 46 of the inductor 41 and an input opposite thereto and the output pad 47 of the inductor 42 and an output opposite thereto respectively are connected to a common ground 45, so that there is no route through which interference signals are transmitted by way of wires.

FIG. 5 shows the experimental results measured by Network Analyzer 8510 XF produced by Agilent Technologies and the calculation results by Momentum that is an electromagnetic field analysis software produced by Agilent Technologies both for the layout pattern as shown in FIG. 4 and a conventional embodiment where there are not disposed the wires 43 and 44 as shown in FIG. 4. The vertical axis of the graph indicates the largeness in the unit of dB of the transfer coefficient between input and output signals from the inductor 41 to the inductor 42 while the horizontal axis thereof indicating frequency. According to FIG. 5, it is found that the transfer coefficient of the layout pattern shown in FIG. 4 reduces by 13.7 dB at the frequency of 2 GHz in comparison with the conventional embodiment. Also, as a result of the electromagnetic field analysis, it is found that the degree to which interference is attenuated at the frequency of 2 GHz is predicted within the error of about 1.3 dB.

In the foregoing, interference conveyed from the inductor 1 to the inductor 2 is explained, but where a linear wire is the subject matter, it causes inductance at a higher frequency, so that the disposition of the wire 3 for reducing the inductive coupling around the inductor 1 allows interference caused by the inductor 1 to the linear wire to be restrained.

The same effect as above is realized by enclosing other inductors and elements or circuits in the vicinity of the inductor 1 in addition to the inductor itself with the wire 3 for reducing the inductive coupling forming a closed loop wire.

Further, the wire 3 reducing the inductive coupling is usable for conveying a DC voltage with AC signals removed therefrom and for ground wiring. FIG. 6 shows such wire 3 reducing the inductive coupling in such use. The DC from a power source 53 connected to a ground 54 passes through the wire 3 reducing the inductive coupling via an AC signals block circuit 52 and a DC potential connection wire 51 a and reaches a circuit 55 via a DC potential connection wire 51 b so as to drive the circuit 55 connected to the ground 54.

The wire 3 for reducing the inductive coupling must be arranged such that AC signals derived from an induced current flow for the purpose of reducing interference while a DC potential is provided in such an arbitrary manner as by floating or from another circuit. Alternatively, the wire 3 may be a route through which a DC flows by interconnecting plural DC wires. However, it is required that a circuit section including the DC potential connection wire 51, the AC signals block circuit 52, the power source 53, the ground 54 and the circuit 55, the Ac signals block circuit 52 is a choke coil and AC signals not derived from the induced current does not flow through the wire 3, for example. Should AC signals not derived from the induced cur-rent flows through the wire 3, the signals are conveyed from the wire for reducing the inductive coupling to the inductor through magnetic fields, so that unwanted signals result in being overlapped on the inductor. The arrangement as shown in FIG. 6 allows a spatial occupancy taken for the wire for reducing the inductive coupling to decrease by the wire width of the power source and the space between the wires, which results in reducing the layout size of the semiconductor device and improving the integration density thereof. This fact is important especially for the semiconductor device whose size is of essence.

Then, an inductor, in which the effectiveness of the wire for reducing the inductive coupling is enhanced by using two-tiered metal layers, is shown in FIG. 7. This wire for reducing the inductive coupling includes two metal layers and a via to vertically interconnect between those metal layers. In FIG. 7, reference numerals 82 and 83 respectively indicate a wire for further reducing the inductive coupling formed on the second metal layer and a via to interconnect between the wires 3 and 82. To note, a wire 11 is formed on the third metal layer and connected to the inductor 1 through a connection wire 15 engaged to a via 12 and formed on the second metal layer as well as a via 16. FIG. 7 is the vertical view of the layout pattern taken along at the same line as FIG. 2. The inductor shown in FIG. 7 is characterized in that more of an induced current flows by reducing inductance of the wire 3 by way of the wire 82 to increase the degree to which interference is attenuated. Herein, in order to avoid a parasitic capacity generated between the wire for further reducing the inductive coupling and the semiconductor substrate increasing, it is arranged such that the overlapped top metal layer and the second metal layer are interconnected by the via 83 without using the bottom metal layer for the wire for further reducing the inductive coupling. As a result, it is confirmed by the electromagnetic field analysis that the degree to which interference is attenuated increases by 0.5 DB in comparison with the case where the wire for reducing the inductive coupling is arranged in one metal layer. The application of such arrangement allows the metal layers forming wires for reducing the inductive coupling to increase so as to enlarge the extent to which interference is attenuated, especially when there is restriction in wire width.

Now, as shown in FIG. 1, the wire 3 for reducing the inductive coupling is disposed around the inductor 1 such that the former circumscribes the latter, which wire may be spirally disposed instead. This also applies to the wire 4.

FIG. 8 shows inductors in which wires for reducing the inductive coupling are spirally disposed. In the drawing, reference numerals 101 and 102 indicate wires for reducing the inductive coupling spirally disposed around the inductors 1 and 2 respectively. The respective wires 101 and 102 take a spiral shape with three coils. Discrete metal layers and vias intervene between the outer peripheral wire and the inner peripheral wire thereof to form a closed loop wire. As the number of coils increases, connection between the respective inductors 1 and 2 and the corresponding wires 3 and 4 increases to increase an induced current flowing through the respective wires 3 and 4. This further restrains interference signals caused by the mutual inductance between the inductors 1 and 2 from being conveyed in comparison with such arrangement as shown in FIG. 1. Accordingly, the provision of the wire for reducing the inductive coupling of spiral configuration further reduces interference signals.

The semiconductor devices having an inductor provided with a wire for reducing the inductive coupling according to the invention as described above is realized as an RF-IC, for example. This RF-IC is typically used along with a power amplifier for transmission, an antenna and a switch in the wireless communication circuit section of a portable radio terminal. The circulatory arrangement of the portable radio terminal including a wireless communication circuit 111 is shown in FIG. 9.

The transmission section of the wireless communication circuit 111 includes a modulator circuit (first circuit) to modulate carrier waves by a base band signal (first signal) sent from an external base band section 113 to gain an RF signal, a power amplifier 110 to amplify the RF signal (second signal) output by the modulator circuit 97 and a low-pass filter 125 to input the RF signal output by the power amplifier 110 through an output matching circuit 120 so as to remove unwanted higher harmonics contained in the RF signal. The frequency of the base band signal such as about 200 KHz is converted into a radio frequency such as about 2 GHz by the modulator circuit 97. In addition, the communication circuit 111 is provided with a switch 140 that is connected to an external antenna 112 to supply the RF signal output from the filter 125 to the antenna 112 upon transmission and input the RF signal output from the antenna 112 upon reception to supply the signal to a reception section. Further, the reception section of the communication circuit 111 includes a band-pass filter 165 to remove undesired disturbing waves contained in the RF signal input from the switch 140, a low noise amplifier 151 to input the RF signal output from the filter 165 through a matching circuit 160 for reception to amplify the signal and a demodulator circuit (second circuit) 152 to demodulate an RF signal (third signal) output from the low noise amplifier 151 to output a base band signal (fourth signal) and supply the signal to the base band section 113. Also, a local oscillator (third circuit) 98 is provided as a common circuit for transmission and reception to generate carrier waves for modulation/demodulation and supply the carrier waves to the modulator circuit 97 and the demodulator circuit 152.

In the above arrangement, an RF-IC 150 is constructed with a high-frequency circuit including the modulator circuit 97, the low noise amplifier 151, the demodulator circuit 152 and the local oscillator 98 integrated. Hereafter, preferred embodiments of the semiconductor devices according to the invention realized as examples of the RF-IC are described.

First Embodiment

FIG. 10 shows the first embodiment of the invention. In this embodiment, inductors provided with wires for reducing the inductive coupling in the modulator circuit 97 are exemplified. In the drawing, reference numerals 61 and 62 respectively indicate inductors, reference numerals 63 indicates a wire for reducing the inductive coupling forming a closed loop wire, reference numeral 64 indicates a modulator, reference numerals 66 a through 66 d respectively indicate buffers, reference numerals 67 a and 67 b respectively indicate base band signal inputs, reference numerals 68 a and 68 b respectively indicate carrier wave inputs, reference numeral 69 a and 69 b indicate RF signal outputs and reference numeral 70 indicates a capacitor. Base band signals orthogonal to each other are input to the base band signal inputs 67 a and 67 b. The respective orthogonal base band signals are of bipolar differential signals whose polarity is inversed to each other. Carrier waves (local oscillation signals) whose phase differs by 90 degrees are input to the carrier wave inputs 68 a and 68 b. The respective carrier waves are also of bipolar differential signals whose polarity is inversed to each other.

The circuit including the inductors 61 and 62 along with the capacitors 70 forms a differential low frequency wave pass filter. The base band signals input from the base band signal inputs 67 a and 67 b are respectively input to the mixers 65 a and 65 b through the buffers 66 a and 66 b while the carrier waves input from the carrier wave inputs 68 a and 68 b are respectively input to the mixers 65 a and 65 b through the respective buffers 66 c and 66 b. In the mixers 65 a and 65 b, the carrier waves are modulated by the base band signals to turn into the differential RF signals, which are input to the above differential low frequency wave pass filter. To note, the same polar components of differential RF signals orthogonal to each other output from the mixers 65 a and 65 b are connected to each other, in which the RF signals of one polarity are supplied to the inductor 61 while those of the other polarity are supplied to the inductor 62.

The output signals from the mixers 65 a and 65 b respectively contain not only frequency components as desired but also higher harmonic components such as those signals having frequency as two or three times higher as required. For example, when the typical frequency of the RF signal is at 2 GHz, higher harmonic signals are generated at 4 GHz or 6 GHz. The above low frequency wave pass filter is used to remove such higher harmonic components. The RF signals with such higher harmonic components removed therefrom through such filter are output to the signal outputs 69 a and 69 b. It is a differential signal that is input to the inductors 61 and 62, so that there is no worry about interference between those inductors. However, the magnetic field change to which one inductor is subjected has higher harmonic components so as to generate a single-phase interference signal in the other inductors and wires disposed nearby. This interference signal is attenuated by the wire 63 for reducing the inductive coupling that encloses both inductors 61 and 62 to restrain the amount by which such higher harmonic components are conveyed.

The concrete effect brought by the wire for reducing the inductive coupling is confirmed by the electromagnetic field analysis. For example, where the outline of the inductors 61 and 62 is defined as 130 μm in length, 3 μm in width, 3 μm in space and nine coils, the interference signal generated in a wire positioned by 46.5 μm away from the outline of the respective inductors 61 and 62 is attenuated by about 40 dB in comparison with the 4-GHz signal input to the inductors 61 and 62. On the other hand, such interference signal is attenuated by about 45 dB when the wire 63 for reducing the inductive coupling having 6 μm in width and 3 μm in space is disposed around the inductors 61 and 62. Thus, the effect for reducing the inductive coupling improves by 5 dB. The provision of the wire for reducing the inductive coupling enclosing the inductors 61 and 62 in combination according to the present embodiment not taking account of interference allows the layout area to be reduced by as much as the reduced wire width and spatial region in comparison with disposing a wire for reducing the inductive coupling for each inductor.

Second Embodiment

FIG. 11 shows the second embodiment of the invention. In this embodiment, inductors provided with a wire for reducing the inductive coupling in the local oscillator 98 are exemplified. In the drawing, reference numerals 71, 72, 73, 74, 75, 76, 77, 78, 79, 80 and 81 respectively indicate an inductor acting as a choke coil, a wire for reducing the inductive coupling forming a closed loop wire, a resonance inductor of an oscillator, a varactor diode of variable capacity, a capacitor, a transistor, a variable current source to define the operational current of the transistor, a power source voltage to the transistor 76, a frequency controller, an oscillator output and a ground. In this embodiment, the inductor (i.e. choke coil) 71 takes the interfered side.

An oscillation frequency is defined by the frequency of a resonance circuit including the indicators 73, varactor diodes 74 and capacitors 75. When control voltage is provided to the frequency controller 79, the bias voltage charged to the respective varactor diodes 74 changes to change their capacity, which results in the oscillation frequency changing. Since a positive feedback circuit is arranged with the respective transistors 76, an oscillation signal of a frequency determined by control voltage at a desired amplitude is output from the respective outputs 80. The oscillating signals are of differential signals whose polarity is inversed to each other and turn into carrier waves to be supplied to the modulator circuit 97 and the demodulator circuit 152. The inductors (choke coil) 71 provide a DC ground potential to the varactor diodes 74 and block AC signals that are the oscillation signals to convey the signal to the oscillator outputs 80.

Herein, where an interference signal source exists nearby, such signal is conveyed to the inductor (choke coil) 71 to be overlapped on the oscillation signal, with the result that the oscillator outputs unwanted disturbing waves. Further, when the frequency of the interference signal is closer to that of the oscillation signal, the latter fluctuates owing to the drawing effect as described in the Non-Patent Document 3. Such undesired disturbing waves are restrained and such drawing effect is avoided by the disposition of the wire 72 for reducing the inductive coupling.

Further, the wire 72 for reducing the inductive coupling does not take the rectangular shape as shown in FIG. 10, but takes such shape as if tracing the outline of the circuit block to reduce spatial occupancy. As a result of the electromagnetic field analysis, it is confirmed that there is no difference in the degree to which interference is attenuated, irrespective of whether a wire for reducing the inductive coupling is disposed only on the interfered side inductor or only on the interference source side inductor, provided that such conditions as the shape, material and interval between the inductors are the same. Accordingly, when the interfered side indictor such as a variable frequency oscillator is subject to interference from other circuits, the disposition of a wire for reducing the inductive coupling around such inductor reduces interference. Thus, the present embodiment is effective especially when there is no room for disposing a wire for reducing the inductive coupling in the interference source side inductor so that such wire is disposed only in the interfered side inductor.

Third Embodiment

FIG. 12 shows the third embodiment of the invention. In this embodiment, inductors provided with a wire for reducing the inductive coupling in the modulation circuit 97 and the local oscillator 98 are exemplified. The inductors of the modulator circuit 97 take the interference source side while those of the local oscillator 98 take the interfered side. In the drawing, numeral reference 91 indicates an RF variable gain amplifier, reference numerals 92 a and 92 b indicate base band filters, reference numerals 93 a and 93 b indicate base band amplifiers, reference numeral 94 indicates a frequency divider, reference numeral 95 indicates an RF output, reference numerals 96 a and 96 b indicate base band signals, reference numeral 97 indicates a modulator circuit and reference numeral 98 indicates a local oscillator respectively.

The modulator circuit 97 has the same arrangement as that of the first embodiment and the variable frequency oscillator 98 has the same arrangement as that of the second embodiment. The present embodiment exemplifies a transmission circuit of the direct conversion type wherein the frequency of the base band signal is converted into a radio frequency at one time by use of one carrier wave, the operation of which circuit is briefly shown below.

The differential base band signals orthogonal to each other input to the base band inputs 96 a and 96 b are amplified to desired amplitudes by the base band amplifiers 93 a and 93 b and are restricted within the band allowable for wireless communication by the base band filters 92 a and 92 b. On the other hand, where a carrier wave frequency is 2 GHz for example, the oscillation signals of 4 GHz output from the local oscillator 98 are divided into 2 GHz as half as the oscillation signal by a frequency divider 94 so that the differential carrier waves (local oscillation signals) having difference in phase by 90 degrees are output. The differential base band signals orthogonal to each other and the differential carrier waves having difference in phase by 90 degrees are input to a modulator 64. The strength of the four respectively differential signals is amplified by the buffers 66 a through 66 d to be input to the mixers 65 a and 65 b. The mixers 65 a and 65 b respectively perform QPSK (Quadrature Phase Shift Keying) modulation that is one of the quaternary modulation systems. Hereupon, unwanted higher harmonic components such as two-fold and three-fold frequency are output. Those components are blocked by a filter circuit including the inductors 61 and 62 and capacitors 70, so that the desired RF signal is taken out. After the RF signal is amplified by a variable amplifier 91, it is output to an RF output 95.

In the present transmission circuit, the inductors 61 and 62 cause the magnetic field change having such higher harmonic components in the vicinity thereof as mentioned earlier and interference occurs between the inductors (i.e. choke coils) 71 and the inductors 73 as shown in FIG. 12. In order to reduce such interference, the respective wires 63 and 72 for reducing the inductive coupling are respectively disposed to the outer periphery of the modulator circuit 97 and the local oscillator 98. The measurement result shows that undesired higher harmonic components generated by the interference among the inductors and output from the RF output 95 is reduced by 5 dB by the disposition of such wires 63 and 72 to the modulator circuit 97 and the local oscillator 98 in comparison with the prior art wherein there is no such disposition. The present embodiment in which a wire for reducing the inductive coupling is disposed to the interference source side inductor and the interfered side inductor reduces undesired disturbing waves output from the modulator circuit 97.

To note, the structure of the semiconductor substrate according to the above embodiments is not limited to the above bulk type, but may well be SOI (silicon on insulator) substrate or type made from different material such as a Sapphire substrate. Further, the frequency range applicable to the invention is not limited to that as shown in FIG. 5. The invention is applicable not only to spiral inductors described above, but also to arbitrary inductor having the number of coils, the winding direction and the vertical configuration thereof modified. Further, the modulator circuit as shown in the first and third embodiments respectively is of differential type, but may well be of single-phase type, in which a low-pass filter is made of one inductor.

The inductor according to the invention is widely applicable to a matching circuit and an amplifier, etc., besides the above oscillator and filter. There is a case where an inductor may be incorporated in the low noise amplifier 151 and the demodulator circuit 152, though not shown in the figure. In such case, the provision of a wire for reducing the inductive coupling to the inductor as described above reduces interference from the local oscillator 98 or from the transmission side, especially when the communication system in which transmission and reception operate simultaneously is adopted.

In implementation of the invention, there is neither need to adopt a new production method of the semiconductors nor worry about increased power consumption. The reduction of the self-inductance of the inductor and the increased layout area that are side effects of the invention are restrained to the minimum by making the layout design in a proper manner. On the other hand, narrowing an interval between the inductors in accordance with the degree of reduction of interference by the application of the invention increases the integration density of the circuit and allows the wireless communication circuit to be multi-functional. Also, the specifications at the design stage can be eased as much as the reduction of interference, the number of designing processes can be reduced and the production period can be shortened.

According to the invention, the semiconductor devices with inductors reduces interference between inductors caused by a magnetic field generated by the inductors, so that undesired noise signal output is minimized. 

1. A semiconductor device comprising: a first circuit to modulate a carrier wave by way of a first signal to output a second signal whose frequency is higher than a frequency of said first signal; a second circuit to demodulate a third signal by use of said carrier wave to output a fourth signal whose frequency is lower than a frequency of said third signal; and a third circuit to generate said carrier wave, wherein at least one of said first, second and third circuits has at least one inductor, and wherein said at least one inductor is provided with a closed loop wire enclosing said one at least inductor.
 2. The semiconductor device according to claim 1, wherein said at least one inductor and said closed loop wire are formed on one isolation layer of a semiconductor substrate.
 3. The semiconductor device according to claim 1, wherein said closed loop wire is adopted for flowing a direct current.
 4. The semiconductor device according to claim 1, wherein said at least one inductor is provided with another closed loop wire enclosing said at least one inductor.
 5. The semiconductor device according to claim 1, wherein said closed loop wire is of multi-coiled spiral shape.
 6. The semiconductor device according to claim 1, wherein at least one circuit element is disposed in addition to said at least one inductor within an enclosure of said closed loop wire.
 7. The semiconductor device according to claim 1, wherein said at least one inductor is disposed in said first circuit.
 8. The semiconductor device according to claim 1, wherein said at least one inductor is disposed in said third circuit.
 9. A semiconductor device comprising: a first circuit to modulate a carrier wave by way of a first signal to output a second signal whose frequency is higher than a frequency of said first signal; a second circuit to demodulate a third signal by way of said carrier wave to output a fourth signal whose frequency is lower than a frequency of said third signal; and a third circuit to generate said carrier wave, wherein at least one of said first, second and third circuits has at least one inductor, and wherein said at least one inductor is provided with a wire for reducing inductive coupling generated through mutual inductance.
 10. The semiconductor device according to claim 9, wherein said wire is a closed loop wire enclosing at least said at least one inductor.
 11. A semiconductor device comprising: a circuit to convert a base band signal as input into a radio signal by modulation and to convert said radio signal as input into said base band signal by demodulation, wherein said circuit is provided with at least one inductor, and wherein said at least one inductor is provided with a wire for reducing an inductive coupling generated through mutual inductance.
 12. The semiconductor device according to claim 11, wherein said wire is a closed loop wire enclosing at least said at least one inductor. 